Ultra short wave receiver



B. TREVOR 222,035

ULTRA SHORT WAVE RECEIVER I Filed May 19, 1936 70 RECEIVER ANTENNA ISECONDARY PR/MA RY FILTER \NVENTOR BETRAM TREVOR ATTORNEY Patented May28, 1940 I UNITED STATES arcane ULTRA SHORT WAVE RECEIVER BertramTrevor, Riverhead, N. Y.,

assignor to Radio Corporation of America, a corporation of DelawareApplication May 19, 1936, Serial No. 80,492

.14 Claims.

This invention relates to ultra short radio wave systems.

One of the objects of the present invention is to provide an ultra shortWave receiver capable of receiving an extremely wide modulation-band,such as might be used in the transmission of television programs. Such amodulation band may be of the order of about three million cycles.

A further object is to provide a band pass transformer having balancedprimary and secondary circuits of the coaxial line type.

For achieving the foregoing object, there is employed a novel type ofband pass transformer, for passing the energy received by the antenna toa balanced detector circuit, to which are fed locally generated highfrequency oscillations from a resonant line controlled oscillator. Theoutput of the detector is designed to feed into a cascaded intermediatefrequency amplifier which, in turn, may be coupled to a second detectorcircuit from which the output is amplified and arranged .to pass into asuitable utilization circuit.

Various features of the present invention relate to a novel coaxial orconcentric line type of band pass transformer, and to the concentricfrequency control line for the local oscillator, which, althoughdescribed with particular reference to the receiver circuit, are not ofthemselves limited thereto, since they are capable of being used inother systems.

Other objects and features, and their advantages will appear more fullyhereinafter in connection with the accompanying drawing, wherein Fig. 1shows a preferred embodiment of the invention in connection with areceiving circuit for receiving ultra short waves of the order of 1.7meters, although it is to be understood that the invention is notlimited to this particular wavelength. Fig. la is a cross-sectional viewof the coaxial line transformer of Fig. 1 along the lines 1a'1a.

' Referring to the drawing in detail, there is shown in Fig. l a bandpass transformer comprising a plurality of pairs of coaxial orconcentric lines I, 2; I, 3; 4, and 4, 6. It will be noted that thereare two pairs of lines oppositely and symmetrically located with respectto a central metallic plate I, and that the conductors on one side ofplate I are extensions, or on the same straight line with the conductorson the other side of the plate. Since the coaxial lines on each side ofthe central metallic plate l are located next to one another, it isproposed, for

purposes of convenience and design, to employ' a common outer conductorfor both pairs of lines on the same side of the center plate and toaccomplish this result the outer conductors are made to have a squareform, as shown in Fig. 1a, which. is a cross sectional View of the 5band pass transformer along the line Ia-Ia. The outer conductors l and 4are made of seamless, square, brass or copper tubing and are arranged tobe symmetrically positioned with respect to their associated innerconductors. These square tubings are designed to extend beyond the endsof the inner conductors and to be closed at such ends in order tocompletely shield the entire system. The inner conductors 2, 3; and 5,ii, are joined together at their ends by means of variably balancedcondensers C2, C2. Each half of the band pass transformer, looked uponfrom the center toward the ends, is a resonant circuit completelybalanced with respect to ground. Both resonant circuits comprisinghalves I, 2; I, 3; and 4, 5; 4, 6 are coupled together at their innerconductors by means of connections 8 and 9 which couple together theinner conductors extending on the same straight line, preferablysubstantially symmetrically with respect to the center plate I, asshown. It will thus be seen that we have the equivalent ofa transformercomprising two balanced resonant circuits coupled together, eachresonant circuit being equivalent, electrically, to a parallel tunedcircuit. A damping resistance R, of the correct value, is shownconnected across the adjacent ends of the inner conductors of one of thebalanced tuned circuits in order to assist in obtaining the desired flattop characteristic of the transformer; that is, so thatboth balancedhalves 4, 5; 4, 6; and I, 2; I, 3; may effect a band pass transformer.In certain instances it may be desirable to provide an additionaldamping resistance across the opposite adjacent 4,0 ends of the innerconductors of the other tuned resonant circuit, although this is notnecessary in the present case. The band pass transformer, justdescribed, is coupled to a suitable input circuit, herein designated theantenna, through a pair of connections Iii which are conductively joinedto the inner conductors 2, 3 of one-half of the band pass transformer.This last balanced circuit comprising I, 2; I, 3 will thus be designatedthe primary of the transformer, and 5 the other balanced tuned circuitto which the output leads II are connected, the secondary of thetransformer.

-"The energy received from the antenna over connections I0, and passedon to connections II through the band pass transformer, is fed into thegrids of a pair of push-pull connected detector tubes I2, I3 to whosecathode is coupled a line controlled high frequency oscillator I4. Itwill thus be observed that the received signal waves are applied to thegrids of tubes I2, [3 in push-pull (i. e., the signal waves are appliedto the grids out of phase with respect to each other), while the localoscillations generated by oscillator I 4 are applied to the cathodes ofthe tubes I2, IS in push-push (i. e., in parallel relationship). In theoutput of the detector tubes I2, I3 there is a transformer L3L4 whoseprimary winding L3 is balanced with respect to ground but whosesecondary winding L4 is unbalanced with respect to ground and coupled tothe intermediate frequency amplifier. A balanced condition of theprimary winding L3 is maintained by the electrostatic shield I5 whichsymmetrically surrounds the coil. A portion of this shield is positionedbetween L3 and L4. It should be noted that windings L3 and L4 comprise aband pass transformer for passing the desired wide modulation band on tothe intermediate frequency amplifier.

The local oscillator. I4 is stabilized as to frequency by a concentricline comprising an outer conductor Ill and an inner conductor II, whichare conductively coupled together at one of their adjacent ends andcapacitively coupled together by capacitor C1 at their other adjacentends. The control electrode of oscillator I4 is connected to the outerconductor I6 through the parallel combination of a condenser I8 and aresistor I9.

The anode of oscillator I4, it should be noted, extends through a pipe23 to the inside of inner conductor II, near its end and extends, bymeans of a connection 2i, through the entire length of the innerconductor and then to the source of power supply +250 volts. It ispreferred that the anode be b31-passed to the pipe 20, as shown. Thecathode of the oscillator I4 connects with the inner conductor I'I nearits middle, while the heater element extends through a pipe 26, also tothe inside of the inner conductor I'I near the middle, and then to theheater source of supply. The reasons for this manner of connection mayperhaps be more readily explained by comparing the oscillator tube I4and the line circuit I6, I"! to the well known three point Hartleyoscillator circuit as described in United States Patent No. 1,356,763,granted October 26, 1920. Such circuit comprises an inductance whoseextreme terminals are coupled to the anode and control electrode andwhose cathode is connected to a point intermediate the ends of theinductance. In the present case, the inner conductor I? acts as theinductance of the Hartley circuit, and it is to the lower end of thisinductance I6 that the anode of oscillator I4 extends. The controlelectrode of oscillator I4, it should be noted, is connected to theouter conductor which is at ground potential. Since this outer conductorI6 is conductively connected to the inner conductor,

or inductance II, at its other end, we thus have a connection from thecontrol electrode to the end of inductance I! which is opposite the endof the inner conductor connected to the anode. The cathode of oscillatorI4, however, extends and is effectively joined for all purposes, to themiddle of the inductance I'I, since it enters the inside of inductanceI'I near its middle, as previously described and as shown in thedrawing. In order to maintain both the cathode and the heater element ofoscillator I4 at the same radio frequency potential, so that theyfluctuate simultaneously and in the same phase with respect to oneanother, the heater leads are brought to the middle of the line atsubstantially the same location to which the cathode element is brought,and extends through the inside of inner conductor I! to the heatersupply. In order to maintain, the cathode and heater elements of thedetector tubes I2 and I3 at the same radio frequency potential, theconnections to these elements are also brought to substantially a singlelocation on the inner conductor for the same reasons hereinabovementioned with respect to the identical elements of the oscillator tube.It will be noted, however, that the connections to the heater andcathode elements of the detector tubes I2 and I3 are brought to a pointon the inner conductor I'I near the conductively connected ends ofconductors I6 and IT. This is because the cathodes of detectors I2 andI3 present an appreciable resistance load to the line circuit IS, IT,and the circuit arrangement must be such that this resistance load doesnot destroy, to a great extent, the oscillator stability of the tube I4produced by the concentric line IS, II. It is desired that the cathodesof the detector tubes be coupled to the inner conductor as near the lowpotential end of the line I5, I I, in this case the conductively joinedend, as possible, but this point of connection cannot be too close tothe low potential end for the reason that the detectors require anappreciable exciting voltage to enable them to function as such, and thecloser this point of connection is placed toward the low potential end,the less this exciting voltage for the detector will be. It will thus beseen that for efficient operation of the detectors, there will be apoint of entrance to the inner conductor from the cathodes of thedetector tubes I2 and I3, which will not be too near the low potentialend of the resonant line I6, I! to interfere with the efliciency of thedetectors, nor too near the high potential end of the line I6, H tointerfere with the frequency stability of the control line circuit. Thecathodes of the detector tubes, it will be noted, are in circuit withground through a suitable bias resistor R. Metal pipes 20, 20'. 20 servethe useful purpose of preventing undesired capacity effects between theouter conductor I6 and the leads which extend within the pipes, and forthis reason the pipes extend slightly beyond the outer surface of theconductor I6.

Coupled to the output of detectors I2, I3 is a cascaded intermediatefrequency amplifier system, not shown.

In setting up and making test runs on the receiver, it may be desirableto supply a local signal generator which is arranged to feed locallygenerated oscillations over a concentric cable to a point near thereceiving antenna. In this way the signal generator can be made toradiate energy into the receiving antenna which allows band width andsensitivity checks to be made on the antenna receiver combination. Thisset-up is provided mainly as a help in properly tuning the receiver.

It will be appreciated that the invention is not limited to the precisearrangement of parts shown and described, since various modificationsmay be made in the circuit elements without departing from the spiritand scope of the appended claims.

It will also be understood that the term ground" used in thespecification and appended claims is not limited to an actualearthedconnection but includes any point of zeroor relatively fixedradio frequency potential. What is claimed is: I

- 1. A bandpass transformer having a primary comprising a pair ofresonator circuits, each resonator circuit includingan inner and anouter and secondary being placed end to end, an input Srcircuit coupledto the inner conductors of said primary, an output circuit coupled tothe inner conductors of said secondary, and a connection couplingtogether each inner conductor of-said primary with the inner conductorof said secondary which extends on the same straight line.

2. A band pass transformer in accordance with claim 1, including aresistance connected across said inner conductors of said secondary.

3. A band pass transformer having a primary comprising a pair ofresonator circuits, each resonator circuit including an inner and anouter conductor, said inner and outer conductors of said pair beingconductively coupled together at one end, said inner conductors beingcapacitively coupled together and said outer conductors conductivelycoupled together at their other ends, a secondary for said transformerhaving a similar arrangement of a pair of resonator circuits arranged insuch manner that the inner conductors and outer conductors of both saidprimary and secondary are extensions of one another, the conductivelycoupled ends of both said primary and secondary being placed end to end,an input circuit coupled to the inner conductors of said primary atpoints substantially near and symmetrically located from theconductively coupled ends, an output circuit coupled to points on theinner conductors of said secondary near the capacitively coupled endsthereof, and a connection coupling together each inner conductor of saidprimary with the inner conductor of said secondary which extends on thesame straight line.

4. A balanced resonant circuit comprising a pair of adjacent resonatorcircuits, each having an inner and a parallel outer conductor, means forconductively coupling together all of said conductors at one end, a pairof variable condensers coupling together the other ends of said innerconductors, a damping resistor directly connected across said last endsof said inner conductors for providing a desired frequencycharacteristic for said balanced resonant circuit, means for groundingsaid outer conductors, and input and output circuits coupled to saidinner conductors.

5. A balanced resonant circuit comprising a rectangular metalliccontainer, an electrically conductive partition separating saidcontainer longitudinally into two halves to form square tubularconductors, an inner conductor coaxially positioned in each half, ametal plate conductively coupling together all of said inner and outerconductors, and means for variably coupling together capacitively thefree ends of said inner conductor, said #square tubular conductorsextending beyondthe capacitively coupled ends of saidin'n'er conductors.

6. A balanced resonant circuit comprising a pair of adjacent resonatorcircuits, each having an inner and a parallel outer conductor, means forconductively coupling together all of said conductors at one end, meansfor capacitively coupling together the inner conductors of said pair ata location removed from said one end, anda resistor connected acrosssaid inner conductors near said last location.

'7.'A transformer comprising a first balanced resonant circuitcomprising a pair of adjacent resonator circuits, each having an innerand a parallel outer conductor, means for conductively coupling togetherall of .said conductors at one end, and means for capacitively couplingtogether the inner conductors of said pair at a location removed fromsaid one end, a second balanced circuit having a similar arrangement ofa pair of resonator circuits, and connections from the inner conductorsof said first balanced circuit to the inner conductors of said secondbalanced circuit, an input circuit coupled to said inner conductors ofsaid first balanced circuit, and an output circuit coupled to said innerconductors of said second balanced circuit.

8. A resonantcircuit arrangement comprising a rectangular metalliccontainer, an electrically conductive partition separating saidcontainer longitudinally into two portions to form substantially squaretubular conductors, an inner conductor coaxially positioned in eachportion, means forconductively coupling together all of said inner andouter conductors at one location, whereby each of said square conductorswith its associated inner conductor forms a tuned circuit, and means forcapacitively coupling together the inner conductors of both portions atanother location removed from said first location.

9. A resonant circuit arrangement comprising a rectangular metalliccontainer, a metal sheet separating said container into two portionseach having the form of substantially square tubular conductors, aninner conductor coaXially positioned in each portion, means forconductively coupling together said inner and outer conductors at onelocation, and means for capacitively coupling together the innerconductors of both portions at another location removed from said firstlocation, a second similar resonant circuit arrangement, a connectionfrom each inner conductor of one resonant circuit arrangement to thecorrespondingly located inner conductor of the second resonant circuitarrangement, an input circuit coupled to the inner conductors of oneresonant circuit arrangement, and an output circuit coupled to the innerconductors of the other resonant circuit arrangement.

10. In combination, a tuned circuit comprising an inner and an outerconductor conductively coupled together at one end, another tunedcircuit also comprising an inner and an outer conductor coupled togetherat one end, a direct connection from a point on one inner conductorintermediate its ends to a point on the other inner conductorintermediate its ends, an input circuit coupled to one of said innerconductors at another point intermediate its ends, and an output circuitcoupled to the other of said inner conductors also at another pointintermediate its ends.

11. A resonant circuit arrangement comprising a pair of coaxial lineseach having an inner and an outer conductor, means for. conductivelycoupling together said inner and outer conductors at one location, andmeans for capacitively coupling together the inner conductors of bothlines at another location removed from said first location, a secondsimilar resonant circuit arrangement, a connection from each innerconductor of one resonant circuit arrangement to the correspondinglylocated inner conductor of the second resonant circuit arrangement, aninput circuit coupled to the inner conductors of one resonant circuitarrangement, and an output circuit coupled to the inner conductors ofthe other resonant circuit arrangement.

12. A balanced resonant circuit comprising a pair of adjacent resonatorcircuits, each having an inner and a parallel outer conductor, means fordirectly coupling together all of said conductors at one end, a pair ofvariable condensers coupling together the other ends of said innerconductors, a damping resistor connected across said last ends of saidinner conductors for providing a desired frequency characteristic forsaid balanced resonant circuit, means for connecting said outerconductors to a point of relatively fixed radio frequency potential, andinput and output circuits coupled to said inner conductors.

13. A balanced resonant circuit comprising a pair of adjacent resonatorcircuits, each having an inner and a parallel outer conductor, means forconductively coupling together all of said conductors at one end, andmeans for capacitively coupling together the inner conductors of saidpair at a location removed from said one end, a resistor connectedacross said inner conductors near their other ends, an input circuitcoupled to said inner conductors of said pair at points substantiallysymmetrically located from one end, and an output circuit coupled tosaid inner conductors of said pair at differently located points whichare intermediate the ends of said inner conductors and alsosubstantially symmetrical with respect to said same last end.

14. In combination, first and second tuned circuits each comprising apair of conductors disposed one within the other, means couplingtogether the conductors of each tuned circuit at one end, means couplingthe outer conductors of said tuned circuits together and to ground,Whereby the inner conductors of said tuned circuits are coupled togethernear said same end, a connection including a reactance between the innerconductors of said tuned circuits at a location removed from said lastends, and a resistive connection also between said inner conductors at alocation removed from said last ends.

BERTRAM TREVOR.

